(Invited) Dye-Sensitized Photoelectrochemical Cells with Hydrogen-Atom Transfer Co-Catalyst for Oxidative Lignin Decomposition

Abstract

The lack of selectivity of oxidative-cleavage is one of prime issues for decomposition of lignin, because of the harsh reaction environments, such as high temperature and high pressure, in general. Dye-sensitized photoelectrochemical cells with a homogenous hydrogen-atom transfer co-catalyst with Ruthenium-complex based sensitizer as a photocatalyst (e.g. RuC ((bis-2,2′-bipyridine)(2,2′-bipyridine-4,4′-dicarboxylic acid)Ru(II)) (HAT-DSPEC), was suggested as an alternative and this system exhibited the conversion efficiency of over 90% at 24 hour illumination (AM 1.5G) although these metal-complex based sensitizers, having relatively low values of absorption coefficient, generally are not cost-effective and stable enough.In this study, for highly stable HAT-DSPEC process, metal complex sensitizer was replaced by organic dye(5-[4-(diphenylamino)phenyl]thiophene-2-cyanoacrylic acid, L1) which has high stability and molar absorption coefficient. Also three kinds of organic nitroxyl mediators (HAT) was used such as 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), 4-Acetamido-TEMPO (ACT) and 9-azabicyclo[3,3,1]nonan-3-one-9-oxyl (Keto-ABNO). Each HATs (TEMPO, ACT and keto-ABNO) showed different reactivity and conversion efficiency (about 65%, 60% and 88%). In HAT-ODSPEC(organic dye-sesitized photo-electrochemical cell), Keto-ABNO showed highest conversion efficiency with 2-ol(S,G). This HAT-ODSPEC process provides a unique foundation to perform selective C−C bond cleavage for real lignin conversion technologies.